202 FLORIDA GEOLOGICAL SURVEY-I 3TH1 AN NUAL REPORT

But saw-grass being evergreen, the foliage present at any one time represents more than one year's growth, so that the proper procedure would be to first mow down a small patch of it in midwinter, and then cut and weigh a measured area from the same patch a year later.
 Pcat prairies. These are basins reaching a few to several feet below the ground-water level which have become filled with peat, and are covered with herbaceous vegetation other than saw-grass, presumably on account of the water being purer or at least less calcareous than in the saw-grass marshes. They are more common in the lake region than elsewhere. In the course of development from lake to peat prairie the vegetation has of course undergone considerable change, beginning with none at all and passing through the aquatic and marginal types above mentioned. That growing on the surface of the peat at present is much like that of some of the lake margin prairies described on the next page, except for the frequent occurrence of dense clumps of bay (Magnolia glanca) and other broad-leaved evergreens, a few rods in diameter. The most characteristic plants have been listed in the Third Annual Report (pp. 274-275), and do not need to be repeated here. The herbs are mostly grasses and other monocotyledons. The peat in such places is among the purest to be found anywhere.
 Basin prairies (fig. 16). The flat-bottomed lakes which drain off at intervals through subterranean outlets, in the Hernando hammock belt and farther north, are carpeted when dry with herbaceous vegetation that has not been carefully studied, but consists largely of plants whose indigeneity is under suspicion, for they grow also in places that have obviously been altered artificially. The most characteristic seem to be dog-fennel, Enpatorium capillifolinn, and a grass, Anastrophus paspaloides, as stated in the Third Annual Report, page 261. The weediness of the vegetation is doubtless largely due to the fact that such areas have long been closely grazed by cattle and she.ep.
 Lake margii prairies (fig. 26). Some of the larger lakes that are so shallow that a small change in water level makes a great difference in the position of the shore line have the area between high and low water covered with grassy vegetation similar in aspect to that just mentioned, and containing some of the same plants and